1. Grape Root Growth and Physiology in Relation to Environment and Vine Crop Load
Lakso, Eissenstat, Xu, Dunst
May 15, 2003- May 14, 2007
USDA Special Funding: Cornell University-Viticulture Consortium Research Grants Program and New York Wine/Grape Foundation.

The long-term goals of the work are to: (a) improve ourunderstanding of the regulation of grape root growth and respiration in relation to the environment (soil temperature, water, nutrients), and to varying crop load, and (b) integrate these root factors into a model of carbohydrate supply/demand. Ultimately, we want to optimize the management of both the top and the roots of the grapevine for sustained production of desired yields and fruit quality.

Objectives for 2006 Growing Season:

Our previous root growth studies have shown that at least 3 years of seasonal root growth monitoring to make any solid conclusions about field studies. Also, we have completed the controlled environment potted-vine studies on the effects of temperature and soil moisture outlined in the current and previous reports and publications, but these results need to validated under field conditions. Therefore the 2006 objectives are to:

1. Monitor seasonal fine root production and survival in a mature vineyard crop load trial of constant pruning level for the 3rd year to determine the sustained effects
   of adjusted crop loads on the production and lifespans of Concord grape fine roots.

2. In the same study determine the effects of crop load (and soil drying if the season is dry enough) on root respiration, membrane leakage, carbohydrate/nitrogen concentrations of grape roots.
3. Take soil cores under mature Concord grapevines in the crop load study pre-veraison to estimate the total maximum amounts of fine roots per vine to allow the calculation of the total carbohydrate requirements of the root system.
4. Determine normal daily patterns of root respiration and responses to canopy shading (to reduce carbohydrate supply to the roots) in mature field Concord vines.

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2. Root responses to soil moisture deficits in fruit crops

a) Towards a better understanding of soil moisture deficits on shoot and root physiology

Eissenstat, DM, Neilsen D, Neilsen G.

Pennsylvania State University and Pacific Agri-Food Research Centre, Summerland, BC.

April 1, 2002-March 31, 2005. Funded by Washington Tree Fruit Research Commission and matching funds from AAFC-MII.

Studies are examining the effects of different irrigation practices on apple tree physiology in Summerland, British Columbia. The effects of deficit irrigation and partial root zone drying on root dynamics and shoot physiology will be examined over three years. The feasibility of using novel irrigation practices to reduce total irrigation, reduce vegetative growth and improve fruit quality will be assessed. This research will link root growth and mortality to apple water uptake, shoot water potential and leaf stomatal conductance and photosynthesis.

b) Seasonal patterns of root physiology and dynamics of Vitis vinifera cv Merlot on two rootstocks under different levels of irrigation.

Smart DR, Eissenstat DM, Bauerle TL.

Pennsylvania State University and University of California, Davis
Funded by Western Viticulture Consortium, July 1, 2002 - June 30, 2006
The long-term goals of the work are to: (a) develop our understanding of the relationships of grape root development and structure to root function (water and nutrient uptake, storage of carbohydrates and nutrients), to the environment (soil temperature, water, nutrients); to root pests; and to cultural practices (irrigation, mulching, pruning or crop regulation) and (b) integrate these belowground factors with effects on the aerial part of the vine into a model of carbohydrate supply/demand. Ultimately, we want to optimize the management of both the top and the roots of the grapevine. Initial emphasis is placed on wine grapes (Vitis vinifera) in the Western United States, because of the lack of information, the availability of an established vineyard with multiple controlled irrigation treatments arranged in a randomized complete block design, and an excellent research facility with staff to oversee cultural practices.

Justification and Importance of Proposed Research:

Optimal management strategies for any system require a thorough understanding of the main parts of the system. A critical concept in viticulture is that of vine "balance". By that we mean that vine growth (both top and roots) are in proper balance with each other and with the crop so that we obtain sustained yields of the desired fruit quality without excessive vegetative growth or debilitation. We must know what is occurring in the root system to optimize that "balance." To achieve high-quality wines, how does the timing and distribution of roots influence the most effective spatial and temporal distribution of irrigation and nutrients? Conversely, how does the timing and distribution of irrigation and nutrients influence root distribution and physiology? This proposed project is designed to examine seasonal root dynamics and physiology of two grape rootstocks that differ in overall vigor (1103P, V. berlandieri X V. rupestris and 101-14 Mgt V. riparia X V. rupestris) in response to deficit irrigation. Examination of the effects of deficit irrigation on grape not only provides information towards the conservation of water, but can also aid the vineyard manager in improving fruit quality and controlling excessive vegetative growth without decreasing yield.

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3. Collaborative research: Linking leaf and root traits to ecosystem structure and function in a common garden study of 14 temperate tree species

P. Reich¹, D. Eissenstat³, J. Oleksyn^{1 2}, S. Hobbie¹, J. Chorover⁴, M. Tjoelker⁵, O. Chadwick<sup>6

1</sup>Univ. Minnesota, ²Polish Academy of Sciences, ³Penn State, ⁴University of Arizona, ⁵Texas A&M, ⁶UC Santa Barbara

June 1, 2002 - May 31, 2006 NSF DEB-0128944 Ecosystems Program

We propose to test a series of hypotheses about the mechanisms whereby woody plant species alter ecosystem processes and properties. Plant traits have long been considered key controls of ecosystem functioning and can influence nutrient cycling, decomposition, productivity, and pedogenesis. However, most of our current understanding of plant effects on ecosystem structure and function comes from comparisons among species or communities where separating effects of climate, soils, or stand age from those of vegetation is difficult. Furthermore, these comparisons have focused primarily on the aboveground component of the ecosystem. To understand the connections between aboveground and belowground processes and the role of the species in controlling ecosystem structure and function requires common garden experiments. Yet common garden experiments with long-lived species are rare, and those that do exist contain too few species to allow robust generalizations. We propose a study of a unique, replicated common-garden experiment of 33-year old monoculture stands of 14 temperate tree species in Poland. Preliminary data show that in just 30 years plants have caused major changes in soil properties such as pH, and forest floor and mineral soil calcium (Ca), nitrogen (N) and carbon (C). The large number of species, the stand age, the replicated experimental design, as well as established collaborations with Polish scientists, make this site uniquely suited to testing important hypotheses related to interspecific variation in leaf and root traits and how these traits influence ecosystem structure and function. We propose to test several interwoven hypotheses about the links between tissue and ecosystem level properties and processes: (1) Plant species are characterized by predictable "syndromes" of interconnected leaf and fine root traits such that species with low metabolic rates (e.g., low photosynthesis, respiration, and nutrient uptake) have dense structure (e.g., low specific leaf area and low specific root length), low nutrient concentrations, and low turnover rates, and vice versa. (2) Species differences in tissue-level traits translate into large differences among species in ecosystem structure (e.g., canopy and root system mass, forest floor accumulation). For example, species with dense, long-lived, low-nutrient fine roots and foliage will have large aboveground and belowground biomass (i.e., large canopies and root systems) and large forest floor organic matter accumulation. In contrast, species with thin, short-lived, high-nutrient fine roots and foliage will have low canopy and root system biomass and accumulate little forest floor mass. (3) Species with small canopies and root systems promote rapid rates of ecosystem processes (production, decomposition and N mineralization) per unit mass of tissue, while species with large canopies and root systems have low rates of ecosystem processes per unit mass of tissue. Therefore, despite large species effects on ecosystem structure, species will converge in their effects on ecosystem processes when those processes are measured on a per unit area basis. (4) Plant species impose long-term constraints on biogeochemical cycling and pedogenesis by their direct impact on litter chemistry and decomposition, soil Ca and Al pools, and soil pH. High pH promotes microbial biomass and activity, stimulates decomposition of litter and fast-cycling soil organic matter (SOM), but stabilizes slow-cycling SOM. Low pH increases the rate of SOM leaching and podzolization, and shifts the plant-available pool of lithogenic cations from Ca to Al. To test these hypotheses, we will examine: 1) above- and belowground tissue and ecosystem physiology, structure and productivity; 2) litter and soil C and nutrient cycling; and 3) soil chemistry and pedogenesis. Our planned measures in 33-year-old tree species monocultures over a multi-year period will provide a rare opportunity to link individual species traits (above- and belowground) and ecosystem processes such as decomposition, productivity, nutrient cycling and soil pedogenesis in a controlled, replicated experiment with a large number of long-lived species.

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4. Using Phylogenetically Independent Contrasts to Examine Temperature Acclimation of Root and Mycorrhizal Fungal Respiration Among Organisms from Broad Latitudinal Gradients

David M. Eissenstat and Roger T. Koide, Penn State University

February 1, 2003 - January 3, 2006. Funded by NSF IBN-Ecological and Evolutionary Physiology.

Temperature is a major constraint on mycorrhizal root metabolism in many environments. In cold climates, temperatures in the spring restrict root metabolism and nutrient acquisition. In the summer in temperate and tropical climates, unshaded soils may reach temperatures that cause excessive carbohydrate metabolism unless root acclimation occurs. The central objective of this proposal is to examine how latitude of origin affects plant root and mycorrhizal fungal respiratory responses to soil temperature. These investigations will use phylogenetically independent contrasts (contrasts using distinct evolutionary lineages) to permit general inferences on plant and mycorrhizal fungal responses to temperature as a function of latitude of origin. The research will focus on four, interrelated hypotheses associated with organism response to temperature. Does diurnal temperature variation affect an organism's ability to acclimate to temperature? Under conditions of no acclimation, do plants and mycorrhizal fungi from higher latitudes exhibit higher respiration than those from lower latitudes when measured at the same temperature? Under conditions where acclimation occurs, do plants & mycorrhizal fungi from high latitudes exhibit less acclimation to high temperature (i.e., excessively metabolize carbohydrates) than those from lower latitudes? Are the independent mycorrhizal fungal or plant respiratory responses to temperature the same when the organisms are measured in symbiosis? The use of multiple, distinct evolutionary lineages of both fungi and plants will provide new insight into how organisms respond globally to both average temperatures and temperature variation.

This work has several opportunities for broader scientific impacts. Global climate change is an area of intense interest to both scientists and government policy makers. The Intergovernmental Panel on Climate Change predicts a 1.4-5.8 °C increase in global surface temperature by 2100, using atmospheric models that assume increases in atmospheric CO2 will lead to increases in ambient temperature, which increases soil respiration, causing a positive feedback. Mycorrhizal root respiration represents the dominant source of soil respiration in many soils. If mycorrhizal roots acclimate to increases in temperature, than predicted increases in surface temperatures may be overestimated.

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5. The Ecology of Root Lifespan in Temperate Trees
Eissenstat, D.M.

August 1, 2006 - July 31, 2009. Funded by NSF IOB-Environmental and Structural Systems Cluster

Despite its importance, variation in root lifespan among species and in response to changes in the environment is poorly understood. Relatively few species have been examined and rarely have multiple species been compared in a common environment. The work proposed will examine the root lifespan of 12 tree species that vary widely in root diameter, root tissue density and potential growth rate using state-of-the-art approaches. Trees were transplanted as 1-yr-old seedlings in replicated plots in a common garden approximately nine years ago. Variation in root lifespan will be related to plant potential growth rate, root structure (specific root length, diameter, tissue density) and root N concentration. Do roots and leaves share parallel suites of traits commonly associated with their lifespan? Three hypotheses are proposed that attempt to explain what controls and constrains root lifespan: the “Starch depletion hypothesis” (SDH) of Marshall and Waring, the “Resource optimization hypothesis” (ROH) and a new hypothesis proposed here, which is referred to as the “Metabolic activity hypothesis” (MAH). The Starch depletion hypothesis assumes that a finite amount of stored carbohydrates (starch) is deposited at root formation and that the rate the carbohydrates are depleted by root respiration determines the lifespan of the root. The Resource optimization hypothesis assumes that root lifespan is optimized to provide the greatest benefit in terms of water and nutrients for the least cost (usually measured in carbon) over the lifespan of the root or cluster of roots. The Metabolic activity hypothesis suggests that root lifespan is mainly governed by metabolic rate; roots with higher respiratory activity live shorter lives than those with lower respiratory activity. Three experiments are proposed to help distinguish which of these three hypotheses best explains patterns of root lifespan. The first experiment proposes creating fertile patches which do not become depleted. These patches should increase the efficiency of nitrogen acquisition and also increase metabolic rate. If root lifespan is increased in the patch, then ROH is supported. If root lifespan is decreased then either SDH or MAH is supported, depending on how quickly the roots die in relation to their starch reserves. Respiration and nonstructural carbohydrates (including starch) of the roots of the different species will be examined as a function of root age in a second experiment. The third experiment examines the importance of current photosynthate on root lifespan of 1st-order roots by pulse-labeling carbohydrates with 13C. Collectively these experiments should greatly increase our understanding of the ecology of root lifespan.

This study will have several broader impacts. A better understanding of root lifespan will be valuable to those attempting to model ecosystem carbon cycles because of the important link root turnover has in this process. Many of the trees proposed to be examined in this study are forest dominants in much of eastern hardwood forests. Better understanding of their root lifespan will be useful to forest managers as well as investigators of climate change. This study will provide strong support for the training of graduate and undergraduate students in research.

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6. Large Herbivore Mediation of Vegetation Response to Climate Change in the Arctic
Eric Post, David Eissenstat, Mads Forchhammer, Yiqi Luo.

The classic research topic in ecology of whether plant productivity and community composition are governed by species interactions or abiotic factors is relevant to ecosystem response to climate change. Arctic ecosystems have been a major focus of climate change studies because they have the potential for substantial feedback on climate through changes in plant species composition and carbon balance that might influence atmospheric CO2 concentration. Ecologists have long asserted that vertebrate herbivores exert considerable influence on plant biomass, productivity, soil nutrient dynamics, and species composition of the plant communities in which they forage. Alone or in combination, these influences may mediate vegetation productivity response to climatic warming, especially in arctic and sub-arctic ecosystems, where vegetation productivity is characteristically nutrient limited. By conducting controlled experiments involving temperature manipulations inside and outside of caribou- and muskox-proof exclosures in an arctic field site in West Greenland, this project will quantify the influences on vegetation productivity and plant species interactions of natural herbivory and artificial warming. After erecting 6, 800m2 permanent exclosures in June 2002, we began our warming and exclosure experiment in June 2003. After 3 years, our initial results indicate contrasting influences of herbivory and warming on aboveground productivity in deciduous shrubs, graminoids, and forbs; and contrasting influences of herbivory and warming on biomass of leaves and stems in deciduous shrubs. We propose to test several hypotheses about the differential influences of herbivory on the productivity responses of shrubs, forbs, and graminoids to warming. These hypotheses are based on our preliminary data. We will test these hypotheses by doubling the number of experimental and control plots and the length of the warming treatment for the next 3 years. Additionally, we will quantify belowground responses including root growth (using ingrowth cores and minirhizotrons installed in 2005) and root respiration. Moreover, to gain mechanistic insight into primary productivity responses to our treatments, we will quantify soil moisture, temperature and the supply of macronutrients including nitrate, ammonium and phosphate, as well as plant N and P content, photosynthesis and water potentials in experimental and control plots. We will use our data to modify the Terrestrial Ecosystem model (TECO) to examine critical processes in regulating interactive responses of plant growth and nutrient dynamics to grazing and warming in the Arctic. This effort will synthesize our multiple hypotheses about the species-specific effects of herbivory and warming on plant productivity and community dynamics.

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7. Effects of Nitrogen Saturation on Root Senescence in Forest Plantations
David Eissenstat, Zhengquan Wang¹, Dali Guo<sup>2

1</sup>Northeast Forestry University, Harbin, China
²Peking University, Beijing, China

Root N has been negative correlated with root lifespan among 11 tree species in a common garden in Poland and among 26 species among tall grass prairie species. We are testing the hypothesis that root N leads to higher root metabolism which leads to more rapid root senescence. The question is being addressed in an ash plantation (Fraxinus mandshurica Rupr.) in the Maoershan Forest Research Station (45o21' - 45o25' N, 127o30' - 127o34' E) of Northeast Forestry University, in Heilongjiang, China. Patterns of decline in root respiration and root N will be assessed as a function of root age for fertilized and unfertilized trees. Estimates of membrane leakage and other aspects of root oxidant production and detoxification will be assessed. This project is part of a larger study of Drs. Wang and Guo, which will determine the effects of N addition on ecosystem processes.